Any shop that sells the boots can order them for you or you can find them through Full Tilts website. (http://fulltiltboots.com/ski-boot-parts/soul-parts/hardware
). And yes, if they are too worn you do need to replace them for two reasons. First, the shop, normally for liability, has to test the binding after mounting it. If the sole is to worn, the boot normally pre-releases or can cause issues with the toe height of some bindings. Second, if you wear through the replaceable soles and into the plastic of the boot, then the boot is no good anymore. You dont want a gap between a new sole and the plastic if that makes sense. They cost 40 dollars and are 9 screws to replace.